1. Field of the Invention
The present invention relates to refrigeration systems using different refrigerants that dissolve lubricant, and with compressors having a casting for storing oil delivered by a pump for lubrication of their bearings, and more specifically to a method for controlling compressor oil pressure in the systems where oil is returned to the compressor from the evaporator.
2. Background of the Prior Art
Oil is usually used to lubricate refrigeration compressors. The oil pressure of a compressor must be sufficient to support the minimal necessary amount of oil lubricant. If the oil pressure falls below a pressure necessary to support that minimal required amount of lubricant, the compressor can be damaged. That is why refrigeration systems have a special device to turn the compressor off when the pressure of the oil in the system reaches the minimum level. The oil from the compressor is evacuated with the refrigerant vapor. After the evaporation of the liquid refrigerant has taken place in the evaporator of the refrigeration system, the oil returns to the compressor either by refrigerant vapors or separately from the refrigerant.
In U.S. Pat. No. 3,978,685 by M. Taylor, issued Jul. 14, 1975, the oil returns to the compressor with the refrigerant vapors from the evaporator. In this case a certain amount of liquid refrigerant can enter the compressor along with the oil. This cannot be evaporated by the same method as in the evaporator. The oil pressure drops and a blocking device turns the compressor off. A certain amount of time and special preparations are required to restart the compressor again.
A similar situation is described in U.S. Pat. No. 4,631,926 by Goldstein, et. al., issued on Dec. 30, 1986, which states that when the oil carrying liquid refrigerant separates from the vapor, the refrigerant moves to the compressor through a special thermal exchange heater. A significant amount of the refrigerant returns with the oil to the compressor due to the existing inertia of the system, which supports a temperature level of the mixture of the oil and the refrigerant. It leads to the same disadvantages of the system as in U.S. Pat. No. 3,978,685.
The present invention relates to a method of controlling the oil pressure in a compressor in order to allow it to work without interruption. This can be accomplished by the use of the following method. Practice shows that the oil pressure changes step-wise when the liquid refrigerant is accessing into the compressor. At the beginning, the pressure does not drop significantly and stays higher then the allowed minimum. As the liquid refrigerant continues to enter the compressor, the oil pressure drops significantly and reaches a critically low level. When the oil along with the liquid refrigerant is prevented from entering the compressor immediately after the first drop of pressure, the oil pressure will be elevated. The elevation in pressure is due to the extraction of the excess amount of liquid refrigerant from the oil in the compressor. Thereafter, the compressor can continue to work without interruption.